The present disclosure relates to an antenna, and a method of constructing an antenna for an integrated circuit, in particular, for a mm-wave integrated circuit (IC).
Mm-wave systems are becoming more and more important. For example, communication systems that operate in the tens to hundreds of GHz range are becoming important. Furthermore, TeraHertz imaging applications are emerging as important in Homeland Security applications, mainly because TeraHertz radiation can image through clothing. As explained below, the antenna leads for an IC that operates in this frequency range has traditionally been a problem. There is a need in the art for an IC packaging method that includes an antenna, and that is relatively inexpensive.
FIG. 1 illustrates a typical package used for microwave RF ICs. The RF chip (RF-IC) 121 is bonded to an insulating package substrate 103. Bond wires 112 are attached from the chip pads (IC pads) 123 to package bond pads 111 that are on the top of the package substrate 103. The package bond pads 111 connect through the package substrate 103 to package pins 105 on the bottom of the package substrate. The package pins 105 are soldered to board traces 107 on a printed circuit board 101 that form connections to voltage supplies, antennas and/or other signal interconnects. The RF-IC is encapsulated by an encapsulation 115.
Antennas for microwave frequencies are relatively large, and do not fit on-chip. Therefore they typically are built or mounted on the printed circuit board, and are connected to the packaged chip by board traces.
When designing a complete RF system using a chip, there are a variety of unwanted parasitic passive capacitances and inductances that must be accounted for. FIG. 2 shows a reasonable approximation for an equivalent circuit of a conventional RF IC lead for a signal passing from the chip to the package, especially an antenna connection. The drawing shows some of these capacitances and inductances. These capacitances and inductances include the IC pin capacitance to ground (around 1 pF), the bond wire inductance (around 1 nH), the package capacitance (around 10 pF), the package inductance (around 1-5 nH), the board inductance and the board capacitance, both of which have values that are a function of the trace length(s). Note that the traces may be in the form of transmission lines. Up to a given frequency, depending on the exact values of the parasitic capacitances and inductances, all of these capacitances and inductances need to be taken into account when connecting say an on-chip power amplifier to a board mounted antenna. For typical present-day packages, frequencies up to of the order of 5 GHz are possible using conventional packaging techniques.
At mm-wave frequencies, the antennas are smaller and it is possible to place them on-chip. However, to date, due to the small vertical dimensions of the typical fabrication processes used, the bandwidths achievable for these antennas are very narrow. While smaller than microwave antennas, they still consume significant chip area. For instance at 60 GHz, a quarter wave length on chip is around 400 um.
It is desired to produce an RF-IC at mm waves, e.g., at around 60 GHz. At such mm-wave frequencies, the circuit shown in FIG. 2 acts as a lossy low-pass filter. Such conventional packaging techniques as shown in FIG. 1 thus cannot be used due to the high loss engendered by the parasitic capacitances and inductances. Expensive or hand crafted solutions must be used to achieve the off and on chip connections at mm-wave frequencies. This results in very expensive mm-wave systems. Such costs prevent such systems from being widely deployed. The high cost is due to the low level of integration and hence the cost of the relatively large number of inter-module connections required. For example, a typical receiver would require a separate antenna to LNA (low noise amplifier) connection, a LNA to mixer connection, and a local oscillator to mixer connection.
Complete “systems on a chip” are becoming possible on silicon at mm-wave frequencies. With a system-on-a-chip, the only off-chip connection at the high frequency remains the antenna or antennas.
Flip-Chip bonds are known in the art, and such bonds provide for direct connection from the substrate of the chip to another substrate, e.g., via solder bumps. Thus, one option for connecting antennas to an RF chip is to “flip-chip” bond a silicon substrate of a mm-wave RF IC onto a low-loss substrate that may hold antennas. Direct connection from chip to substrate can yield low inductance connections. The problem with such an approach is the increased manufacturing cost associated with the flip-chip process, and the associated low yield of the manufacturing process.
Thus there is a need in the art for a relatively low-cost method to connect one or more antennas to an RF IC at mm-wave frequencies. Such a relatively low-cost method should use conventional packaging techniques.